Protective device for high-tension circuits



July 1, 1930. K. NIEMANN 1,768,779

PROTECTIVE DEVICE FOR HIGH TENSION CIRCUITS Filed Aug. 23, 1927 //v YENTO I? KARL N/cw/y/wv ATTORNEYS Patented July 1, 1930 UNITED STATES KARI;NIEM'ANN, OIBEBIIIN-BIEMENSSTADT, GERMANY PROTECTIVE DEVICE FORHIGH-TENSION CIRCUITS Application filed August 28, 1927, Serial 170.214,878, and in Germany August 2, 1926.

This invention relates to improvements in high tension circuitsespecially used in connection with X-ray apparatus, and has pargicularreference to a protective device there- It is known to protect operatorsof X-ray apparatus and patients being treated therewith against injurieswhich may be caused by touching wires under high tension, by

10 providing circuit breakers within the circuit of the hi h tensiontransformers which are actuated y phenomena caused within the circuitsunder high tension by the touching thereof. Such arrangements, however,are often too late in than operation, since all of these breakersoperate with a certain retardation.

An object of the present invention is to avoid the great disadvantage ofthe above mentioned arran ement.

In its preferre embodiment the discharge gap or the primary windin of atransformer, in the secondary win ing of which the discharge gap ismounted, 1s bridged over the primary winding of the high tensiontransformer in such a way that the current is disconnected from thelatter through the operation of the discharge ga This causes thedisappearance of the hig tension. In the operation of this system thedangerous high tension is eliminated at the same moment that there is adisturbance of the potential equilibrium caused by touching the wires ofa high tension system, or which is better et, the high tension issuppressed through t e operation of this system caused by the electricspark which occurs immediately before .the touchin of such a system. Theshort circuit whic is thus caused breaks the circuit immediatelyafterwards, but this feature is only for the purpose of protecting thepower circuit.

In the drawings- Figures 1 and 2 dia ammatically represent differentcircuits or carrying out the present invention.

In Figure 1, s is the high tension winding of the transformer t asapplied, for instance, to X-ray apparatus. High tension conductors leadfrom the terminals of the winding and on the other, of t e associatedmetal coatin f or A conductor leads from each .0 the plates f and f tothe discharge gap 7' Each flange is connected to one end of thedischarging gap f which may be of any suitable type wherem theelectrodesof the discharging ap arecconstituted by material such that t eelectrical discharges occurring upon excessive potentials cause a shortcircuit, or an arc discharge. The two electrodes are also connected tothe ends of the primary winding p of the high tension transformer t sothat, in comparison with the parts of the X-ray apparatus which carryhigh tension current, said electrodes are at a potential that ispractically equal to the earth potential.

If, through inadvertence or any other unforeseen cause occurring duringthe o eration of the apparatus,a rounding of one of the two high tensionines should take place (across an ohinic resistance or by means of aspark occurring between the earth and the line) or if the high tensionline, during theoperation of the apparatus, "should come-in contact itha body of cons'iderable capacity which is insulated from the earth, thed1stribution of potential in the hi h tension circuit changes materiallywith t e result that considerable potentials occur at points of the hightension circuit, r, and at the discharge gap '7', between which nootential or only a low potential previous y existed, so that thedischarge gap f is actuated. This discharge, however, short circuits theprimary winding p of transformer t. Consequently the line potential iscut off and therefore the high tension winding 8 is currentless; or, atleast, the potential falls to such a value that it is no longerdangerous. It is thus seen that by the employment of a discharge gap asa short circuiting means, the operation is an instantaneous one, incontrast with mechanical circuit breakers whose operation is retardedbecause of the inertia of the parts and requires an appreciable periodof time to be effected.

The discharging circuit may also be arranged within another line circuitsuch as an auxiliary winding, the short circuiting of which causes thediscontinuance of the high tension. Instead of a single discharge gap,several may be employed. In any case, however, they are to be soinserted that they are able to indicate potential differences which areeffective during defective operation of the installation.

In contra-distinction to the known arrangements, the present inventionis effective when the circuits under high tension are touched, evenbefore these lines or wires or parts are subjected to high tension andthis touching still exists at the moment of the high tension connection.

It has proved to be advantageous not to employ the discharge gap or lineto operate as short circuit-breaker as indicatin means for the shift ofpotential, but to assign this function to a special discharge circuitcausing the discharge in the short circuiting discharge line. In thusdisencumberin the main discharge line, it may be so deslgned that itsshort circuiting efiect is as efiicient and as nearly perfect aspossible at the inception of the discharge.

The discharge circuit which is sensitive to potential shifts is suitablyconnected with one terminal to a point of the high tension circuit whichduring normal operation has a certain earth potential, such as, forinstance, the center of the high tension winding or any other artificialzero point such as the center of an ohmic resistance bridged over thehigh tension terminals, whereas the other terminal may be connected tothe ground or to a point of the transformer low tension winding; inother words, to a point the potential of which is not materially alteredduring disturbances of the potential equilibrium in the high tensioncircuit.

The problem to operate the short circuiting discharge circuit when andonly when the auxiliary or indicating discharge circuit is operated, maybe solved in such a way that the auxiliary discharge circuit is providedwith a certain capacity which discharges itself upon over-bridging ofthe indicating circuit into the short-circuiting discharge circuit.

It is essential for the satisfactory functioning of the present devicethat, in accordance with the above mentioned features, theshort-circuiting discharge circuit is connected to the high tensioncircuit in such a manner that it operates only with potential shiftsoccurring in the high tension circuit.

This requirement is essential because if, for instance, it were possibleto also ener ize the discharge circuit by means of high requencyoscillations generated by the spark caused immediately before thetouching1 of parts of an oscillatory circuit connecte to the dischargecircuit, the device would operate continuously, inasmuch as it werecoupled to X-ray apparatus with rotating high tension rectifier or withany other device or arrangement containing a spark circuit.

In such cases in which there is danger of influencing the dischargecircuit by means of eventually generated sparks, it is advantageous totake other special precautions in order to avoid harmful electricaloscillations or to prevent their impression upon the discharge circuit.This is best efiected by means of a choke coil inserted immediately infront of the dischar e gap. Also, apparatus may be connecte with thechoke coil which affords the conductors a convenient equalization pathin front of said coil.

Figure 2 represents such an arrangement. The terminals of high tensionwinding 8' are bridged over by any kind of device adapted to create anartificial zero point, as for example, by means of two or moreseriesconnected condensers 0 c. The low tension winding p is connectedto the spark circuit f, the electrodes of which are formed by the twocopper blocks k is. A thin metal foil m is placed between these blocksand is covered on the one side with a thin insulating layer such aspaper, for instance. The metal foil m is connected over a choke coil dwith a midpoint of condensers 0 c, in other words, with a point of earthpotential. The drawing does not show special condensers parallel to thetwo spark gaps which are formed by the metal foils and thecopper-blocks, since the capacity of the electrodes is sufficient to theattainment of the desired results.

If now, through any possible cause a potential shift occurs in the hightension circuit, the center of the condenser battery takes acorresponding potential with respect to the ground. One of the two sparkcircuits formed by the metal foil and copper block or k respectively, isput into operation, the metal foil fuses or evaporates and thus causesan arc discharge between the copper blocks 70 and [0 thereby shortcircuiting the primary winding of the high tension transformer. Anyother spark occurring in the high tension circuit or between partsincluded in the high tension circuit does not sufiice to operate thedischarge circuit k, 70*, even if it is capable of generating strongelectric oscillation for these oscillations would take the line of leastresistance for them which leads over the condenser battery, and theywould not the detour leading to the discharge circuit which isobstructed for them by the choke c o1l d. If the capacity of a and 1ssultably 5 dimensioned, the choke coil 0 may, in many 4 cases, bedispensed with. It is also possible to use discharge circuits orcontaining easily ionizable What is claimed is: m 1. A protective devicefor X-ray apparatus comprising a transformer having a primary and asecondary winding; electrodes connected to the terminals of t e primarywinding and forming a spark gap across such wmding, leads connected -tothe terminals of the secondary winding, and capacitive couplings betweensaid leads and the spark gap circuit of said primary wind 1 v go Aprotective device for X-ray apparatus comprising a transformer having aprimary and .a secondary winding e ectrodes connected to the terminalsof the primary winding and forming a spark gap across such windi twocondensers connected to the terminals of the secondary a thin foilterminal located in said spark gap, and a choke coil connectedin seriesthro h one terminal to said thin pfoil termina, the other terminal ofsaid coil being connected midway between said condensers. I 3. A safetydevice for high tensionsystems comprising a transformer the primary :5winding of which is connected through regulating devices to the mainsupply circuit and the secondary of which is connected to thehightension system, a spark gap comprising three electrodes, aconnection from 0 one electrode to one line of the main supply circuit,a connection from another electrode to the other line of the main su plycircuit, and a connection from the third 7 electrode to the secondawinding ofthe 5 transformer, said electro es so spaced with .relation toeach other that an arc travelling from said last mentioned electrode toeither of the other two electrodes, due to a partial or com lete groundin the high tension system, w1 cause an arc to be created between saidfirst two mentioned electrodes to short circuit the incoming supplylines.

KARL NIEMANN.

